I’ll keep this shorter than Derek Zoolander’s attention span (zing!). Zoolander 2 is not good. Not among the worst movies ever, but ultimately not funny. I’m a big fan of the original, and the call backs and characters kept me interested for a while, but after about an hour I was just wishing it would hurry up and get over with so I could say I finished it. The acting, writing, directing and story are exactly what you expect, not the worst ever, but peaking at average.
The only reason to see Zoolander 2 is if you watched the original so much that you feel you owe it to them (that was me). The saddest part is the same part that was sad about Anchorman 2; I still quote the original to this day, but won’t remember a single line from the sequel.